Cascade’s Remediation Cost Avoidance Series
Oct 31, 2017 -
If you take a look at the past two decades, it’s easy to see the amount of advancements within environmental remediation. After twenty years of the industry’s work performing in situ groundwater remediation, new technologies and best practices have resulted in the avoidance of the costs associated with failed or partial remedies. As with any young industry, this type of learning curve is expected, as are the technology improvements that eventually result from shared lessons learned. This is especially true with regard to the challenges of subsurface hydraulics.
To help explain these cost avoidance tactics, and to package them in a way that our employees and customers can easily understand, we created a series of webinars. Cascade’s Remediation Cost Avoidance webinar series focused on two key aspects of remedial design: site characterization & conceptual site model development, and delivery & technology optimization for contaminant treatment. If you’re interested in any of the information contained within the webinar, we’ve provided a quick breakdown of each, as well as links to in-depth breakdowns we provided on our blog, below.
A CSM (Conceptual Site Model) is the primary tool for decision-making. The decision at a jobsite, for most projects, is only as good as the CSM and the ability of the decision makers to understand and incorporate it. A common reason for underperforming or failed remedies is most often an inadequate or incorrect CSM. Money spent on development of a good CSM is an investment in cost savings during remediation and long term monitoring. High Resolution Site Characterization tools like WaterlooAPS, COREDFN, MIHPT, and UVOST are industry proven technologies that help refine CSMs.
Being able to understand and manage your site data is an important consideration during the high resolution and traditional site characterization that’s used to develop your CSM. Your measure of remediation success ultimately depends upon the quality of decisions, which are based on data interpretation.
If you are using or planning on using data and analysis systems (such as C-Techs EVS) for high resolution and traditional sampling data interpretation in support of your remedial design, it is important to develop a level of confidence in the data presented.
Most modeling applications appeal to as many users as possible, and in doing so make it easy for novice users to simply accept ‘default’ settings (aka the ‘black box’). For some purposes, such as creating an initial map to explore the data, this is fine. However, data interpolation, prediction, and general uncertainties tend to overestimate lows and underestimate highs. For this reason and others, it’s always best to work with and consult professionals trained in the hydrogeological sciences.
Webinar 3 – Chlorinated Solvent Matrix
Cascade has developed a matrix of sub surface delivery technologies that are instrumental in achieving our goal of accurate, refined site models. The matrix represents both best practices and lessons learned, and having worked on hundreds of sites across the U.S. over the last 15 years, covering a wide range of lithologies, amendments, and delivery approaches, we have sound basis in creating it. No other field services company or consultant in our industry has worked on more remediation projects. This matrix was developed to help our customers with a wide range of remediation experiences, not to re-invent the wheel. It is meant to help customers benefit from what already has been collectively learned, and get them started in the right direction.
You can can see on the horizontal axis that we have it broken down into Source Zones, Transition Zones, Plumes and Receptors. We have also made a simple break between clays and sands, and the typical remedial objectives for each, from which you can see mass reduction, MNA, and MCLs. On the vertical axis we include in situ technologies or amendments most often applied, and delivery technologies used to apply these amendments in relation to contaminant mass - which we break down into DNAPL, PPM concentrations < 1% DNAPL solubility, and < PPM.
At this time we are looking at mass in groundwater, but based on lithology you can also make assumptions of how much additional mass is sorbed in soil. We have also added a High Resolution Site Characterization section to the matrix since these data developed using these technologies are often critical to selecting both amendments and delivery technologies.
To receive a copy of Cascade’s technology matrix, please contact us and we would be happy to provide it.
The past decade has seen rapid progress in groundwater remediation and an increasing understanding of the capabilities and limitations of potential technologies. Typically, the nature and concentration of the contaminant of concern (COC), as well as the subsurface hydrogeology, dictates which remedy is best suited for the site - though experience has shown that different technologies are needed at different times and locations, and combining technologies may improve overall remedy performance.
The current state of the science based on Cascade’s experience at hundreds of sites across the country with various subsurface geologic and hydrogeologic conditions and contaminant concentrations are discussed.
Based on our experience implementing hundreds of ISCO designs and review of performance monitoring data, we believe ISCO performance can be improved by:
- Not overlooking NAPL or mass sorbed to soils that can require multiple applications to liberate and treat.
- Considering hydraulics and ISCO kinetics in the radius of influence design estimates .
- Using HRSC and not relying just on data derived from monitoring wells data which are insufficient to define target intervals.
- Not injecting through wells at highly heterogeneous sites.
- Paying closer attention field parameters such as distribution, pressure, flows, tooling, and injection approach.
Many types/forms of injectable ISCR products are available, containing a more fine-grain ZVI (micro), ferrous iron and/or reduced minerals. Advanced ISCR reagents take advantage of the fact that fermentation of organic carbon in proximity to iron or iron-bearing minerals increases both reactivity and longevity of the iron component (alkaline/acid balance).
The advancement of including an organic carbon donor with micro-scale ZVI has expanded the range of ISCR applicability such that it can simultaneously treat metals, can be sequentially combined with ISCO, and facilitate post-treatment progression to MNA. ISCR technology is flexible as a variety of ZVI, organic carbon substrates and related additives can be mixed to customize the reagent to site-specific requirements. The capabilities of biogenically formed iron and sulfide minerals are now well known.
Engineered ISCR using ZVI in PRBs is a proven plume treatment technology, and the microscale ZVI used for these barriers can be effectively distribute during injections and requires pneumatic or hydraulic emplacement technologies. The combination of ZVI (abiotic) with electron donors (biotic) offers the potential for rapid chemical degradation of the most accessible contaminants, combined with the longer-lasting bioremediation. The effects of ZVI on biochemistry and indigenous microbial populations appear minimal and may result in sustained reductions in oxidation reduction potential (ORP) that can enhance subsequent anaerobic biodegradation.
Anaerobic biostimulation is the modification of the environment to stimulate existing bacteria capable of bioremediation of chlorinated solvents at low Eh levels and is most appropriate for plume areas where COC concentrations tend to be more dilute and in transmissive zones.
Electron Donor Selection is critical since all do not release hydrogen at the same rate, are not transported through the aquifer at the same rates, and do not have the same electron donor capacity. They are available in soluble and slow release forms, and can be combined both temporally and spatially.
Factors to consider in selection include:
- Contaminant distribution and hydrogeology
- Required persistence/longevity
- Delivery approach
- Size for distribution by advection
- Synergy with bioaugmentation cultures
- Impacts on groundwater pH
The best practice is to use conditioned treatment-area groundwater for substrate dilution or chase water. Groundwater should be extracted, conditioned to a strongly reducing state, and blended with substrate and a bioaugmentation culture in a batch tank.
- Minimizes plume displacement,
- Maintains treatment zone geochemistry,
- Utilizes indigenous microbial cultures to condition water, and
- Quickly establishes optimal conditions in the target aquifer to rapidly develop robust dechlorinating microbial culture.
There has been a wealth of knowledge gained over the last twenty years applying in situ technologies to overcome the long term financial commitments of pump and treat systems. While experts may say that one component of success is more important than another (e.g. delivery versus chemistry), it has become clear that all are of equal performance. As such, for in situ groundwater remediation, success really comes from a sound basis for the CSM, chemistry selection, design based on hydraulics, and residence time.